Current and next generation optical networks are capable of transporting multiple wavelengths on the same fiber by using Dense Wavelength Division Multiplexing (DWDM) technology. Typical systems are capable of transporting 32 or more wavelength channels, at 10 Gb/s rate each.
With capacities exceeding 320 Gb/s per fiber, it is becoming increasingly efficient and economical to perform protection and restoration of traffic in the optical layer. In fact, a major network failure, such a fiber cut or node failure, would impact an extremely large number of client layer devices (e.g., ATM switches or IP routers), making service layer protection intractable.
Many networks today are based upon fiber-ring architectures, as evidenced by the proliferation of SONET/SDH TDM rings all the way from the long-haul backbone to the metropolitan and regional areas. Most large backbone rings represent significant investments on the part of service providers, and expectedly will have longer lifetimes. As a result, ring architectures will clearly play a major role in the evolution of optical networks. Given this large, entrenched base of ring topologies, currently many operators are planning for a migration to equivalent dynamic optical ring architectures. Dynamic optical rings can be defined as fiber rings with dynamic light path provisioning capabilities (such as routing, add/drop, and protection). These optical wavelength routing rings, commonly also referred to as optical add-drop ring multiplexer (O-ADM) rings, will form the mainstay architecture for most metro/regional and even long-haul networks, helping operators ease their transition to future optical (mesh or hybrid ring-mesh) networks.
Since many operators have significant experience in deploying and maintaining SONET/SDH rings, future optical analogs of such time-division multiplexing (TDM) ring switching are of great transitional value. In optical rings, wavelength channels (as opposed to TDM circuits) undergo bypass, add, or drop operations at ring network elements.
Currently, there is a need for fast, scalable optical layer protection mechanisms. Individual channels (timeslots) in SONET/SDH rings (e.g., in Bi-directional Line Switching Ring or BLSR architectures) can be restored in 50 ms in the case of a “clean” ring that does not carry extra traffic, or in 100 ms if extra traffic is present in the ring.
Undoubtedly, optical ring solutions must provide equivalent, or improved, capabilities in order to replace SONET/SDH rings in a timely manner. It is now widely accepted that protection architectures in optical rings must provide restoration times similar to SONET/SDH ring protection architectures (i.e., 50 ms without Extra Traffic, and 100 ms when Extra Traffic is present in the ring).
So far, various optical layer protection mechanisms have been devised for optical rings. It is important to mention that each of these protection architectures is more suitable for specific traffic patterns, in the sense that they optimize the utilization of optical bandwidth for that specific traffic pattern. For example OCh/DPRing architectures work well with hubbed traffic patterns, where a single node in the ring (e.g., the hub) collects traffic from all the other nodes. On the other hand, OCh/SPRing architectures work better for distributed or mesh-like traffic patterns, where there is not a single node that collects all the traffic from the other nodes in the ring. In reality, the traffic pattern in ring networks is neither fully hubbed nor fully mesh-like. Optical rings deployed today by service providers and carriers in real networks provide a SINGLE optical layer ring protection mechanism for the whole ring. This results in under-utilization of the optical bandwidth in the ring—and consequently in a higher cost—because a single protection scheme cannot optimize the ring bandwidth utilization for real traffic patterns.
The present invention is therefore directed to the problem of providing multiple optical ring protection schemes in the same physical ring, in order to better adapt the protection architecture to the traffic pattern in the ring.